Answer:
C. Unbalanced force
Step-by-step explanation:
From first law of motion, an object retains it state of rest or motion unless an unbalanced force acts upon it. Thus, correct option is C.
Option A is incorrect because a force is either a pull or push action on a body.
Option B is incorrect because a balanced force means that net force on the body is zero which would not cause any change in motion.
Option D is incorrect because it does not provide information about force being greater to which force.